Until the 1950's, 35 mm film was commonly used in commercial motion picture theaters, with film frames spaced along the film strip by four perforations. This resulted in a width-to-height aspect ratio of about 1.33 to 1. In the early 1950's, a new format called CinemaScope was introduced wherein each film frame still had a height of nearly four perforations, but had been horizontally compressed. An anamorphic projection lens was substituted for the previous nonanamorphic (nondistorting) lens, to horizontally expand the image by about two times, to project an image having a width-to-height aspect ratio of 2.4 to 1. Substantially all first run motion picture theaters, and most second run theaters installed new projection screens having an aspect ratio of 2.4 to 1 to show CinemaScope. In the 1950's, "ordinary" or non-CinemaScope films continued to use 35 mm film frames spaced by four perforations. However, only a portion of each film frame, occupying a height of about 2.5 perforations, was projected onto the screen. This resulted in the projected image having an aspect ratio of 1.85 to 1. When "ordinary" 35 mm film was shown, masks were installed at opposite sides of the screen to produce a screen aspect ratio of 1.85 to 1.
Over the past four decades, most theaters in large markets (which generate most of the revenue) have installed projectors that project 70 mm film, using a nonanamorphic lens. The 70 mm film has six sound tracks, with four of the tracks lying outside the rows of perforations and two other tracks each lying between a row of perforations and the film frame. Each film frame has a height of about five perforations, resulting in a film frame having an aspect ratio of 2.2 to 1. The projected image has the same aspect ratio. The projected image occupies most of the width of the screen that was initially designed to show CinemaScope, but with masks at opposite sides of the screen to reduce the aspect ratio to 2.2 to 1. If the CinemaScope image and 70 mm image are compared, it would be noticed that the CinemaScope image is wider because it occupies substantially the entire width of the projection screen, but the present 70 mm image is superior. The 70 mm projected image is superior because it has greater definition due to the larger film frame on the film strip, and to the fact that a nonanamorphic lens can be used. Anamorphic projection lenses of all but the highest quality and highest cost produce noticeable distortion of the film frame (linear distortion and especially astigmatism) when projecting it. Up until now, 70 mm film, which produces a bright and clear projected image of a 2.2 to 1 aspect ratio, has been the best image available in commercial motion picture theaters. If an even better projected image could be obtained at low additional expense, this would be of value for the motion picture industry.